1. Field of the Invention
The present invention relates to an internal combustion engine ignition coil apparatus in which a high-voltage cord having a first end portion electrically connected to a secondary coil by means of a high voltage terminal and a second end portion electrically connected to a spark plug is covered by a protective tube, and a leading end portion of the protective tube is engaged elastically with a rim portion for leading out the high-voltage cord.
2. Description of the Related Art
Conventionally, internal combustion engine ignition coil apparatuses are known in which a groove portion formed so as to extend circumferentially is formed on an annular rim portion for leading out a high-voltage cord connected to a secondary coil by means of a high-voltage terminal, and a leading end portion of a protective tube covering an outer peripheral surface of the high-voltage cord engages with the groove portion by elastic force to prevent water from penetrating inside through the rim portion. (See Patent Literature 1, for example.)
Patent Literature 1
Japanese Utility Model Publication No. SHO 54-44163 (Gazette)
In conventional internal combustion engine ignition coil apparatuses, because an inside diameter dimension at the leading end portion of the protective tube is less than an outside diameter dimension at an end surface of the rim portion, as the leading end portion of the protective tube is inserted into the rim portion, at first a leading end surface of the protective tube is inserted in a radially-outwardly expanded state, then the outside diameter dimension of the rim portion decreases suddenly over the groove portion partway through insertion, the outside diameter dimension of the leading end surface of the protective tube also contracts suddenly in response, and the leading end portion of the protective tube engages elastically in the groove portion.
In such internal combustion engine ignition coil apparatuses, engaging force of the protective tube against the rim portion is mainly due to contractive force of the leading end portion of the protective tube, but at the rim portion the protective tube may be repeatedly subjected to thermal stresses due to heat generated by the coil of the ignition coil apparatus itself, heat originating from the internal combustion engine, external air heat, etc., and may also be subjected repeatedly to stresses due to vibration.
Consequently, one problem has been that when the leading end portion of the protective tube is inserted into the rim portion, in the case of a protective tube exhibiting sudden changes due to stress, reductions in the contractive force (the engaging force) and progression of stiffening of the protective tube due to repeated thermal stresses and stresses due to vibration are each accelerated, and in some cases there is a risk that water proofing properties of the protective tube may not be ensured since the protective tube may crack, and the protective tube may move axially and disengage from the rim portion due to the reductions in the engaging force.